LCD devices have been widely used in notebooks, personal digital assistants (PDAs), cellular phones, and other electronic products because the price of LCDs is low and the quality of LCDs is high. LCDs are passive optical devices. Therefore in general a frontlight module or a backlight module needs to be attached to the LCD panel, in order to provide sufficient illumination to make the display of the LCD panel visible at night and to provide a full color display. Generally, the backlight module includes a light source and a diffusion sheet. The diffusion sheet is usually attached below the LCD panel, in order to disperse light beams received from the light source and provide uniform light for the LCD panel. The uniform light enables the LCD panel to display a clear image.
The light source of contemporary backlight modules is usually one of two types: a cold cathode fluorescent lamp (CCFL), or a light emitting diode (LED). The luminescent efficiency of the CCFL is relatively high. However, the CCFL is usually large, and the CCFL consumes more electricity. Therefore, the CCFL is generally only suitable for a large-sized multicolor display requiring high brightness levels. In contrast, the luminescent efficiency of the LED is lower, the size of the LED is smaller, the emitted light of the LED is more focused, and the working lifetime of the LED is longer. In addition, when the LED wears out and needs to be discarded, the LED causes less pollution in the waste disposal cycle. Therefore, the LED is suitable for a monochromatic, electrically efficient, small sized product, such as an LCD panel used in a cellular phone or in a vehicular satellite navigation system.
Referring to FIGS. 6–7, a conventional backlight module 10 includes a flexible printed circuit board (FPCB) 11, a frame 13, three LEDs 15, and a light guide plate 17. The frame 13 includes a side (not labeled) with three notches 132, for receiving the LEDs 15 that are pre-attached on the FPCB 11.
In assembly, the light guide plate 17 is received in the frame 13, and then the FPCB 11 is adhered on the side of the frame 13 by a double-adhesive tape 19. Thereby, the LEDs 15 pre-attached on the FPCB 11 are contained in the corresponding notches 132.
With this configuration, the LEDs 15 pre-attached on the FPCB 11 are located in the notches 132 of the frame 13 without being fixed in position. The LEDs 15 are liable to be displaced if an LCD module employing the backlight module 10 encounters vibration or shock. If the LEDs 15 are displaced, some of the light beams emitted therefrom are liable to be lost. This in turn diminishes the display characteristics of the LCD module.
Accordingly, what is needed is a backlight module that can overcome the above-described deficiencies.